Re: REALLY good introduction to cladistics!!

["David Marjanovic" <david.marjanovic@gmx.at>]

----- Original Message -----
From: <philidor11@snet.net>
Sent: Tuesday, October 23, 2001 1:58 PM

> One of the characters they use to demonstrate that T. rex's share
> a more recent common ancestor with parrots than with caimans
> is the 'heel knob'.  This they note is unique to crocs.  Unless
> you're looking at the question of whether T. rex descended from
> a croc, I thought unique to a group characters were considered
> bad form.
> Is this correct?

Yes.* And read it again, they write explicitely that because *T. rex* and
the parrot share the symplesiomorphy this character is useless, so they have
to use others. Then they come up with dinosaurian and theropodan
syn_apo_morphies.

*It's unique to Crurotarsi and paralleled in mammals and some outgroups,
which doesn't matter in this case.

>  To me, the discussion doesn't lay out the logic of a cladistic
> argument about ancestry,

True. Probably because it would quickly become too long.

> concentrating on animals being treated
> as contemporaries, like T. rex and the parrot.

That really doesn't matter as long as there's no suspicion that *T. rex* is
a direct ancestor of parrots! :-)